The increasing demand to improve vehicular fuel economy and reduce vehicular emissions has led to the development of both hybrid vehicles and pure electric vehicles. Pure electric vehicles may be powered by a battery pack (which is made up of numerous smaller modules or cells), while hybrid vehicles include two or more energy sources, such as a gasoline (also referred to as an internal combustion) engine used as either a backup to or in cooperation with a battery pack. There are two broad versions of hybrid vehicles currently in use. In a first version (known as a charge-depleting hybrid architecture), the battery can be charged off a conventional electrical grid such as a 120 VAC or 240 VAC power line. In a second version (known as a charge-sustaining hybrid architecture), the battery receives all of its electrical charging from one or both of the internal combustion engine and regenerative braking. In either configuration, various parameters associated with the battery pack can be monitored to ensure proper operation.
The determination of the temperature of a cell in a battery (or battery pack) is required to predict a variety of operating parameters in a vehicle powered by such battery. For example, the temperature of a cell in a battery is required to determine the available capacity of the battery. While one method of determining the temperature of a cell in a battery is to put a sensor in contact with the core of the cell in a battery, this method is generally available only in a laboratory setting, as it is placed in a sealed area of the battery that would be inaccessible in a production environment. As a result, the temperature of a cell in a battery is currently determined by directly measuring the temperature of the surface of the cell with a sensor. However, the temperature of the surface of a cell in a battery is often different from the temperature of the core of a cell in a battery.
For instance, the surface temperature of a cell in a battery and the core temperature of a cell in a battery naturally change during a rest period wherein the cell is neither charging nor discharging. Specifically, the surface temperature and the core temperature of the cell will naturally converge to the ambient temperature during a rest period. However, if the rest period is terminated before the surface temperature and the core temperature of the cell converge to the ambient temperature, the surface temperature and the core temperature of the cell will be different. As a result, the use of the surface temperature as a representation of the core temperature may introduce error into calculations involving the temperature of a cell in a battery.